Although the importance of stem cell therapy is recognized, stem cell therapy remains controversial due to the use of embryonic stem cells used for such therapy. Also, stem cells from sources such as bone marrow are difficult to harvest. It would be beneficial to the field if there was a readily accessible source of adult stem cells for harvesting which could impart the same benefits as more controversial and less accessible sources of stem cells. The invention has addressed such a need by the discovery of stem cells that are derived from mammalian hair follicles. A brief background relating to hair provides the basis for hair follicle stem cells of the invention.
Hair growth is a unique cyclic regeneration phenomenon. The hair follicle undergoes repeated cycles of periods of growth (anagen), regression (catagen) and rest (telogen) throughout the life of mammals. The location and function of hair follicular stem cells is a crucial issue for understanding both biology and pathology of hair growth (Oshima, H., et al., Cell (2001) 104:233-245). Label-retaining cells, a characteristic of stem cells, were found to reside in the permanent upper portion of hair follicle, the so-called the bulge area (Cotsarelis, G., et al., Cell (1990) 61:1329-1337).
Recently Taylor, G., et al. (Cell (2000) 102:451-461), reported that hair follicle bulge stem cells are potentially bipotent as they can give rise to not only the hair follicle, but also the epidermis. Other experiments (Oshima, et al., (supra)) also have provided new evidence that the upper outer root sheath of vibrissal follicles of adult mice contains multipotent stem cells, which can differentiate to hair follicle matrix cells, sebaceous gland basal cells and epidermis. Most recently, Toma, J. G., et al. (Nature Cell Biology (2001) 3:778-784), reported that multipotent adult stem cells isolated from mammalian skin dermis, named skin derived precursors (SKPs), can proliferate and differentiate in culture to produce neurons, glia, smooth muscle cells, and adipocytes. However, the exact location of these stem cells in skin and their function were unclear.
It would be useful to the field to isolate stem cells from hair that are related to neural stem cells. According to the invention, a relationship of hair follicle stem cells and neural stem cells has been made.